French President Francois Hollande voiced hope Wednesday that Britons "will remember" their close ties to Europe when they vote in a June 23 referendum on EU membership. 

"We are as united as we have ever been," Hollande said after joining a ceremonial first train ride through the world's longest tunnel as it opened in Switzerland. 

He said he hoped Britons "will remember (that closeness) when the day comes" to cast their votes.